Methods and apparatus for intraoperative assessment of parathyroid gland vascularity using laser speckle contrast imaging and applications of same

ABSTRACT

One aspect of the invention relates to a method for intraoperative assessment of parathyroid gland viability in a surgery. The method includes diffusing a beam of light onto a tissue surface of a parathyroid gland of a patient to illuminate the tissue surface; acquiring images of the illuminated tissue surface, where each of the acquired images includes a speckle pattern; and processing the acquired images to obtain speckle contrast images for the intraoperative assessment of parathyroid gland viability.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This PCT application claims priority to and the benefit of, U.S.Provisional Application Ser. No. 62/440,112, filed Dec. 29, 2016,entitled “LASER SPECKLE IMAGE FOR INTRAOPERATIVE DETECTION OFPARATHYROID GLAND VIABILITY AND APPLICATIONS OF SAME,” by Emmanuel A.Mannoh et al. and U.S. Provisional Application Ser. No. 62/540,767,filed Aug. 3, 2017, entitled “METHODS AND SYSTEMS FOR INTRAOPERATIVEASSESSMENT OF PARATHYROID GLAND VASCULARITY USING LASER SPECKLE CONTRASTIMAGING AND APPLICATIONS OF SAME,” by Emmanuel A. Mannoh et al., whichare incorporated herein in their entireties by reference.

This PCT application is a continuation-in-part application of U.S.application Ser. No. 15/391,046, filed Dec. 27, 2016, entitled“INTRA-OPERATIVE USE OF FLUORESCENCE SPECTROSCOPY AND APPLICATIONS OFSAME”, by Anita Mahadevan-Jansen et al., which is incorporated herein inits entirety by reference.

Some references, which may include patents, patent applications, andvarious publications, are cited and discussed in the description of thepresent invention. The citation and/or discussion of such references isprovided merely to clarify the description of the present invention andis not an admission that any such reference is “prior art” to theinvention described herein. All references cited and discussed in thisspecification are incorporated herein by reference in their entiretiesand to the same extent as if each reference was individuallyincorporated by reference. In terms of notation, hereinafter, [n]represents the nth reference cited in the reference list. For example,[2] represents the second reference cited in the reference list, namely,Sun, G. H., DeMonner, S. & Davis, M. M. Epidemiological and EconomicTrends in Inpatient and Outpatient Thyroidectomy in the United States,1996-2006. Thyroid 23, 727-733 (2013).

STATEMENT AS TO RIGHTS UNDER FEDERALLY-SPONSORED RESEARCH

This invention was made with government support under Contract No.9R42CA192243-03 awarded by the National Institutes of Health (NIH). Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to optical assessments ofbio-objects, and more particularly to methods and apparatus/systems forintraoperative assessment of parathyroid gland vascularity using laserspeckle contrast imaging and applications of the same.

BACKGROUND OF THE INVENTION

The background description provided herein is for the purpose ofgenerally presenting the context of the present invention. The subjectmatter discussed in the background of the invention section should notbe assumed to be prior art merely as a result of its mention in thebackground of the invention section. Similarly, a problem mentioned inthe background of the invention section or associated with the subjectmatter of the background of the invention section should not be assumedto have been previously recognized in the prior art. The subject matterin the background of the invention section merely represents differentapproaches, which in and of themselves may also be inventions. Work ofthe presently named inventors, to the extent it is described in thebackground of the invention section, as well as aspects of thedescription that may not otherwise qualify as prior art at the time offiling, are neither expressly nor impliedly admitted as prior artagainst the present invention.

Approximately 8 million Americans are diagnosed annually with some formof thyroid disease [1], over 92,000 of whom undergo partial or totalthyroidectomy as definitive treatment [2]. An estimated 3% of theseprocedures result in the patient being permanently unable to producesufficient levels of parathyroid hormone for normal serum calciumregulation [3, 4]. Additionally, a significant proportion of patientssuffer from a transient form of this post-surgical hypoparathyroidismand consequent hypocalcemia [5-8], with some studies reportingincidences as high as 47% [8]. Hypocalcemia can lead to cardiacarrhythmias, muscle spasms, tetany and eventually death, and is a hugeeconomic burden for these patients who may require extended hospitalstays or have to take regular calcium supplements for the rest of theirlives to prevent these effects [9]. It is also one of the main causesfor malpractice lawsuits after endocrine surgery [7]. Post-surgicalhypoparathyroidism results from accidental disruption of the bloodsupply to, or accidental removal of, otherwise healthy parathyroidglands, organs responsible for regulating calcium. There are typicallyfour parathyroid glands, which contain calcium-sensing receptors andsecrete parathyroid hormone (PTH) in response to low serum calcium.Parathyroid hormone acts on bone to promote resorption, on the kidneysto reduce calcium elimination in urine, and on the intestines to promotecalcium absorption through the intestinal wall, all of which help toincrease serum calcium [10]. Vascular compromise of parathyroid glandsmay occur after thyroidectomy because of the close proximity of theparathyroid glands to the thyroid. In many cases, the parathyroid glandsderive their blood supply from the same blood vessels that feed thethyroid [11]. Fortunately, devascularized parathyroid glands can besalvaged by autotransplantation—a procedure by which the gland isexcised and transplanted typically into the sternocleidomastoid muscle[12]. However, identifying these glands is challenging and currentlydepends on subjective visual assessment and surgeon experience.Additionally, failure to revive parathyroid function afterautotransplantation has been reported to occur in 14-17% of cases [12,13]. As a result, a surgeon needs to be certain that a parathyroid glandis devascularized, and therefore not viable if left in place, beforecommitting to this procedure.

A number of techniques have been employed to assess parathyroidviability, intraoperatively. A common approach is to look for bright redbleeding after pricking the parathyroid gland with a needle or cuttingoff tiny fragments [14], however care needs to be taken not toirreversibly damage the gland. Topical application of a dilute lidocainesolution has been employed to cause vasodilation in vascularizedparathyroid glands. Any gland that does not swell after application oflidocaine is considered not viable and is therefore autotransplanted.This procedure is risky, since lidocaine can cause paralysis of thevocal cords if it comes into contact with the exposed laryngeal nerve[14]. Intraoperative measurement of PTH is performed routinely inparathyroidectomies to confirm removal of the hyperactive gland. Sincethe half-life of PTH in the blood is 3-5 minutes, removal of aparathyroid gland leads to noticeable decrease in serum PTH within arelatively short amount of time. Based on this concept, intraoperativemeasurement of PTH has also been employed in thyroidectomies [15],however this approach gives no indication of which parathyroid glandmight be compromised. Another approach is to use indocyanine green (ICG)angiography to identify devascularized parathyroid glands. One studyreported that hypoparathyroidism did not occur after surgery inthyroidectomy patients where at least one parathyroid gland wasdetermined (by qualitative assessment of ICG fluorescence) to be wellvascularized [16]. This method requires administration of an exogenouscontrast agent and is limited by how frequently it can be performed.

Therefore, there is a critical need for a real-time, contrast-free andobjective method for assessing the viability of parathyroid glandsintraoperatively.

SUMMARY OF THE INVENTION

One of the objectives of this invention is to evaluate the capability oflaser speckle contrast imaging (LSCI) to distinguish betweenvascularized and compromised parathyroid glands as determined by anexperienced surgeon, in real-time during an endocrine surgery.

In one aspect, the invention relates to a method for intraoperativeassessment of parathyroid gland viability in a surgery. In oneembodiment, the method includes diffusing a beam of light onto a tissuesurface of a parathyroid gland of a patient to illuminate the tissuesurface; acquiring images of the illuminated tissue surface, where eachof the acquired images comprises a speckle pattern; and processing theacquired images to obtain speckle contrast images for the intraoperativeassessment of parathyroid gland viability.

In one embodiment, the method further includes displaying the specklecontrast images of the parathyroid gland in real-time.

In one embodiment, the beam of light is emitted from a light source. Inone embodiment, the light source comprises an infrared laser.

In one embodiment, said acquiring the images of the illuminated tissuesurface is performed with a detector.

In one embodiment, the detector comprises a camera. In one embodiment,the camera comprises an infrared camera or a near-infrared camera. Inone embodiment, the detector further comprises a focus tunable lensattached to the front end of the camera.

In one embodiment, in the speckle contrast images, a perfusedparathyroid gland has low speckle contrast, and a devascularizedparathyroid gland has high speckle contrast.

In one embodiment, said processing the acquired images comprisescalculating a plurality of speckle contrasts from the acquired images ofthe parathyroid gland.

In one embodiment, said calculating plurality of speckle contrastscomprises defining a window with a number of pixels over which a specklecontrast is to be calculated; moving the window across the acquiredimage of the speckle pattern; and at each location, calculating thespeckle contrast as a standard deviation of pixel intensity values aowithin the window divided by a mean intensity value

I

as follows:

$K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$

where the resultant speckle contrast image has values that range from 0to 1, with values closer to 0 representing regions of greater motion(perfusion) and 1 representing regions with no motion.

In another aspect, the invention relates to an apparatus forintraoperative assessment of parathyroid gland viability in a surgery.In one embodiment, the apparatus includes a light source for emitting abeam of light; a diffuser coupled to the light source for diffusing thebeam of light onto a tissue surface of a parathyroid gland of a patientto illuminate the tissue surface; a detector for acquiring images of theilluminated tissue surface, where each of the acquired images comprisesa speckle pattern; and a controller arranged to operate the detector toacquire the images of the illuminated tissue surface, receive theacquired images from the detector, and process the acquired images toobtain speckle contrast images for the intraoperative assessment ofparathyroid gland viability.

In one embodiment, the apparatus further includes a laser pointerarranged in relation to the detector such that its beam is co-localizedwith a center of the field of view of the detector at a distance.

In one embodiment, the apparatus further includes a display fordisplaying the speckle contrast images of the parathyroid gland inreal-time.

In one embodiment, the light source comprises an infrared laser.

In one embodiment, the diffuser comprises a biconvex lens.

In one embodiment, the detector comprises a camera. In one embodiment,the camera comprises an infrared camera or a near-infrared camera. Inone embodiment, the detector further comprises a focus tunable lensattached to the front end of the camera.

In one embodiment, in the speckle contrast images, a perfusedparathyroid gland has low speckle contrast, and a devascularizedparathyroid gland has high speckle contrast.

In one embodiment, said processing the acquired images of theparathyroid gland by the controller is performed with calculating aplurality of speckle contrasts from the acquired images of theparathyroid gland.

In one embodiment, said calculating a plurality of speckle contrastsfrom the acquired images of the parathyroid gland is performed bydefining a window with a number of pixels over which a speckle contrastis to be calculated; moving the window across the acquired image of thespeckle pattern; and at each location, calculating the speckle contrastas a standard deviation of pixel intensity values σ_(s) within thewindow divided by a mean intensity value

I

as follows:

$K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$

where the resultant speckle contrast image has values that range from 0to 1, with values closer to 0 representing regions of greater motion(perfusion) and 1 representing regions with no motion.

In yet another aspect, the invention relates to a method forintraoperative detection of parathyroid gland viability in a surgery. Inone embodiment, the method comprises obtaining speckle contrast imagesof a parathyroid gland of a patent; and displaying the speckle contrastimages of the parathyroid gland in real-time.

In one embodiment, said obtaining the speckle contrast images of theparathyroid gland of the patent comprises diffusing a beam of light ontoa tissue surface of a parathyroid gland of a patient to illuminate thetissue surface; acquiring images of the illuminated tissue surface,where each of the acquired images comprises a speckle pattern; andprocessing the acquired images to obtain speckle contrast images.

In one embodiment, in the speckle contrast images, a perfusedparathyroid gland has low speckle contrast, and a devascularizedparathyroid gland has high speckle contrast.

In one embodiment, said processing the acquired images comprisescalculating a plurality of speckle contrasts from the acquired images ofthe parathyroid gland.

In one embodiment, said calculating plurality of speckle contrastscomprises defining a window with a number of pixels over which a specklecontrast is to be calculated; moving the window across the acquiredimage of the speckle pattern; and at each location, calculating thespeckle contrast as a standard deviation of pixel intensity values aswithin the window divided by a mean intensity value

I

as follows:

$K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$

where the resultant speckle contrast image has values that range from 0to 1, with values closer to 0 representing regions of greater motion(perfusion) and 1 representing regions with no motion.

In a further aspect, the invention relates to an apparatus forintraoperative detection of parathyroid gland viability in a surgery. Inone embodiment, the apparatus has means for obtaining speckle contrastimages of a parathyroid gland of a patent; and displaying the specklecontrast images of the parathyroid gland in real-time.

In one embodiment, said means for obtaining the speckle contrast imagescomprises a light source for emitting a beam of light that is diffusedonto a tissue surface of the parathyroid gland of the patient toilluminate the tissue surface; a detector for acquiring images of theilluminated tissue surface; and a controller arranged to operate thedetector to acquire the images of the illuminated tissue surface,receive the acquired images from the detector, and process the acquiredimages to obtain the speckle contrast images.

In one embodiment, the light source comprises an infrared laser.

In one embodiment, the beam of light is diffused onto the tissue surfaceof the parathyroid gland by a diffuser including a biconvex lens.

In one embodiment, the detector comprises a camera. In one embodiment,the camera comprises an infrared camera or a near-infrared camera. Inone embodiment, the detector further comprises a focus tunable lensattached to the front end of the camera.

In one embodiment, in the speckle contrast images, a perfusedparathyroid gland has low speckle contrast, and a devascularizedparathyroid gland has high speckle contrast.

These and other aspects of the present invention will become apparentfrom the following description of the preferred embodiment taken inconjunction with the following drawings, although variations andmodifications therein may be affected without departing from the spiritand scope of the novel concepts of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file may contain at least one drawing executedin color. If so, copies of this patent or patent application publicationwith color drawing(s) will be provided by the Office upon request andpayment of the necessary fee.

The accompanying drawings form part of the present specification and areincluded to further demonstrate certain aspects of the invention. Theinvention may be better understood by reference to one or more of thesedrawings in combination with the detailed description of specificembodiments presented herein. The drawings described below are forillustration purposes only. The drawings are not intended to limit thescope of the present teachings in any way.

FIG. 1 shows schematically a laser speckle contrast imaging (LSCI)device for intraoperative assessment of parathyroid gland according toone embodiment of the invention.

FIG. 2 shows an LSCI device, according to one embodiment of theinvention, where (a) a picture of the device, and (b) a schematic of animaging end (b) of the device.

FIG. 3 shows speckle contrast images of a microfluidic flow phantom (a)and average line profile perpendicular to flow channel for both lightingconditions (b); white light image of surgical field with OR lights on(c); speckle contrast image with OR lights on (d); speckle contrastimage with OR lights off (e); mean and standard deviation of specklecontrast within parathyroid for both cases (f). Parathyroid glands areindicated with white ellipses and the flow phantom region of interest isindicated with a white rectangle.

FIG. 4 shows images for two examples, each of vascularized (a-d) andcompromised (e-h) parathyroid glands. Left column (a, c, e, g) showswhite light images, with the corresponding speckle contrast images (b,d, f, h) in the right column.

FIG. 5 shows an average parathyroid gland speckle contrast groupedaccording to surgeon's assessment. Speckle contrast is significantlylower (p<0.0001) for vascularized glands (a). Of the compromised glandsonly 5 required transplantation, however no significant difference wasobserved between this sub-group and the compromised glands that wereleft in place (b). Classifying parathyroid glands based on averagespeckle contrast generated an ROC curve with an area under the curve of0.935, and an optimum point with sensitivity and specificity of 92.6%and 90.6% respectively (c).

FIG. 6 shows changes in speckle contrast occurring seconds after bloodsupply ligation. A very noticeable change in speckle contrast (b, d) wasobserved in the same parathyroid gland seconds after tying off bloodsupply to the gland, however no such change was observed in white lightimages (a, c). Images (a) and (b) were taken before, while images (c)and (d) were taken about 30 seconds after ligation of the blood supply.

FIG. 7 shows LSCI detects vascular compromise in healthy parathyroidgland before it is visually apparent. White light image of a parathyroidgland initially thought well vascularized (a) did not agree with specklecontrast image (b). After 15 minutes, this gland was re-evaluated asdevascularized (c) and transplanted. Speckle contrast image (d)supported this assessment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the present invention are shown. The present invention may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this invention is thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like reference numerals refer to like elements throughout.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the invention, and in thespecific context where each term is used. Certain terms that are used todescribe the invention are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitionerregarding the description of the invention. For convenience, certainterms may be highlighted, for example using italics and/or quotationmarks. The use of highlighting and/or capital letters has no influenceon the scope and meaning of a term; the scope and meaning of a term arethe same, in the same context, whether or not it is highlighted and/orin capital letters. It is appreciated that the same thing can be said inmore than one way. Consequently, alternative language and synonyms maybe used for any one or more of the terms discussed herein, nor is anyspecial significance to be placed upon whether or not a term iselaborated or discussed herein. Synonyms for certain terms are provided.A recital of one or more synonyms does not exclude the use of othersynonyms. The use of examples anywhere in this specification, includingexamples of any terms discussed herein, is illustrative only and in noway limits the scope and meaning of the invention or of any exemplifiedterm. Likewise, the invention is not limited to various embodimentsgiven in this specification.

It is understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It is understood that, although the terms first, second, third, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother element, component, region, layer or section. Thus, a firstelement, component, region, layer or section discussed below can betermed a second element, component, region, layer or section withoutdeparting from the teachings of the present invention.

It is understood that when an element is referred to as being “on,”“attached” to, “connected” to, “coupled” with, “contacting,” etc.,another element, it can be directly on, attached to, connected to,coupled with or contacting the other element or intervening elements mayalso be present. In contrast, when an element is referred to as being,for example, “directly on,” “directly attached” to, “directly connected”to, “directly coupled” with or “directly contacting” another element,there are no intervening elements present. It are also appreciated bythose of skill in the art that references to a structure or feature thatis disposed “adjacent” to another feature may have portions that overlapor underlie the adjacent feature.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It is further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” or “has” and/or “having”when used in this specification specify the presence of stated features,regions, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the figures. It is understood thatrelative terms are intended to encompass different orientations of thedevice in addition to the orientation shown in the figures. For example,if the device in one of the figures is turned over, elements describedas being on the “lower” side of other elements would then be oriented onthe “upper” sides of the other elements. The exemplary term “lower” can,therefore, encompass both an orientation of lower and upper, dependingon the particular orientation of the figure. Similarly, if the device inone of the figures is turned over, elements described as “below” or“beneath” other elements would then be oriented “above” the otherelements. The exemplary terms “below” or “beneath” can, therefore,encompass both an orientation of above and below.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itis further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent invention, and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

As used herein, “around,” “about,” “substantially” or “approximately”shall generally mean within 20 percent, preferably within 10 percent,and more preferably within 5 percent of a given value or range.Numerical quantities given herein are approximate, meaning that theterms “around,” “about,” “substantially” or “approximately” can beinferred if not expressly stated.

As used herein, the terms “comprise” or “comprising,” “include” or“including,” “carry” or “carrying,” “has/have” or “having,” “contain” or“containing,” “involve” or “involving” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to.

As used herein, the phrase “at least one of A, B, and C” should beconstrued to mean a logical (A or B or C), using a non-exclusive logicalOR. It should be understood that one or more steps within a method maybe executed in different order (or concurrently) without altering theprinciples of the invention.

Embodiments of the invention are illustrated in detail hereinafter withreference to accompanying drawings. It should be understood thatspecific embodiments described herein are merely intended to explain theinvention, but not intended to limit the invention. In accordance withthe purposes of this invention, as embodied and broadly describedherein, this invention, in certain aspects, relates to methods andapparatus/systems for intraoperative assessment of parathyroid glandvascularity using laser speckle contrast imaging (LSCI) and applicationsof the same.

The LSCI technique analyzes the interference pattern produced whencoherent light is incident on a surface. Minute differences in pathlength created by the light waves scattering from different regions ofthe surface produce bright and dark spots of constructive anddestructive interference respectively, termed as a speckle pattern. Thisspeckle pattern fluctuates depending on how fast particles are movingwithin a few microns of the surface. Blurring of the speckle patternoccurs when the motion is fast relative to the integration time of thedetector. Analyzing this spatial blurring provides contrast betweenregions of faster versus slower motion and forms the basis of LSCI [17].This technique is sensitive to microvascular perfusion and has beenemployed in a variety of tissues where the vessels of interest aregenerally superficial, such as the retina, skin and brain [17]. Many ofits applications have been in laboratory settings for investigatingphenomena such as skin blood flow dynamics in response to externalstimuli [18, 19], and cerebral blood flow in animal models of stroke[20]. Clinically, LSCI and similar techniques have been applied tomonitoring Port Wine Stain laser therapy [21], correlating perfusionwith healing time in burn wounds [22], and measuring cerebral blood flowin patients undergoing brain tumor resection [23]. However, there are nopublished reports on the application of LSCI or any other label-freeoptical method for assessing parathyroid gland viability duringendocrine surgery. Parathyroid glands are densely packed with bloodvessels, given that they secrete PTH to the entire body. Furthermore,their small size (3-8 mm [11]) makes many of these vessels superficial,making these glands suitable targets for assessment using LSCI.

Embodiments of this invention present the LSCI for real-time assessmentof parathyroid viability. Taking an experienced surgeon's visualassessment as the gold standard, LSCI can be used to distinguish betweenwell vascularized (n=32) and compromised (n=27) parathyroid glandsduring thyroid surgery with an accuracy of 91.5%. Ability to detectvascular compromise with LSCI was validated in parathyroidectomies.Results showed that this technique is able to detect parathyroid glanddevascularization before it is visually apparent to the surgeon.Measurements can be performed in real-time and without the need to turnoff operating room lights. LSCI shows promise as a real-time,contrast-free, objective method for helping reduce hypoparathyroidismafter thyroid surgery.

One aspect of the invention relates to a method of using LSCI forintraoperative assessment of parathyroid gland viability in a surgery.The method includes diffusing a beam of light onto a tissue surface of aparathyroid gland of a patient to illuminate the tissue surface;acquiring images of the illuminated tissue surface, where each of theacquired images comprises a speckle pattern; and processing the acquiredimages to obtain speckle contrast images for the intraoperativeassessment of parathyroid gland viability. In the speckle contrastimages, a perfused parathyroid gland has low speckle contrast, and adevascularized parathyroid gland has high speckle contrast.

In one embodiment, the method further includes displaying the specklecontrast images of the parathyroid gland in real-time.

In one embodiment, the beam of light is emitted from a light source. Inone embodiment, the light source comprises an infrared laser.

In one embodiment, said acquiring the images of the illuminated tissuesurface is performed with a detector.

In one embodiment, the detector comprises a camera. In one embodiment,the camera comprises an infrared camera or a near-infrared camera. Inone embodiment, the detector further comprises a focus tunable lensattached to the front end of the camera.

In one embodiment, said processing the acquired images comprisescalculating a plurality of speckle contrasts from the acquired images ofthe parathyroid gland.

In one embodiment, said calculating plurality of speckle contrastscomprises defining a window with a number of pixels over which a specklecontrast is to be calculated; moving the window across the acquiredimage of the speckle pattern; and at each location, calculating thespeckle contrast as a standard deviation of pixel intensity values aswithin the window divided by a mean intensity value

I

as follows:

$K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$

where the resultant speckle contrast image has values that range from 0to 1, with values closer to 0 representing regions of greater motion(perfusion) and 1 representing regions with no motion.

Another aspect of the invention relates to an apparatus (device/system)of using LSCI for intraoperative assessment of parathyroid glandviability in a surgery. In one embodiment, as shown in FIG. 1, theapparatus includes a light source (e.g., a 785 nm diode laser) foremitting a beam of light, and a diffuser (e.g., a lens tube having abiconvex lens) coupled to the light source for diffusing the beam oflight onto a tissue surface of a parathyroid gland (e.g., object) of apatient to illuminate the tissue surface. The biconvex lens diffuses thebeam of light to a spot with a diameter of D on the tissue surface at adistance of H from the edge of the biconvex lens. The light source is aninfrared laser, or the like.

The apparatus also includes a detector (e.g., NIR camera) positionedabove the tissue surface for acquiring images of the illuminated tissuesurface. In one embodiment, the detector comprises a camera. The cameracan be a charge-coupled device (CCD) camera and/or a complementarymetal-oxide-semiconductor (CMOS) camera. In one embodiment, the cameracomprises an infrared camera or a near-infrared (NIR) camera. In oneembodiment, the detector further comprises a focus tunable lens (e.g., azoom lens) attached to the front end of the camera.

The apparatus further includes a computer (controller) arranged tooperate the detector to acquire the images of the illuminated tissuesurface, receive the acquired images from the detector, and process theacquired images to obtain speckle contrast images for the intraoperativeassessment of parathyroid gland viability. In the speckle contrastimages, a perfused parathyroid gland has low speckle contrast, and adevascularized parathyroid gland has high speckle contrast.

The apparatus also includes a display for displaying the specklecontrast images of the parathyroid gland in real-time.

In addition, the apparatus includes a laser pointer arranged in relationto the detector such that its beam is co-localized with a center of thefield of view of the detector at a distance.

In one embodiment, said processing the acquired images of theparathyroid gland by the controller is performed with calculating aplurality of speckle contrasts from the acquired images of theparathyroid gland.

In one embodiment, said calculating a plurality of speckle contrastsfrom the acquired images of the parathyroid gland is performed bydefining a window with a number of pixels over which a speckle contrastis to be calculated; moving the window across the acquired image of thespeckle pattern; and at each location, calculating the speckle contrastas a standard deviation of pixel intensity values as within the windowdivided by a mean intensity value

I

as follows:

$K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$

where the resultant speckle contrast image has values that range from 0to 1, with values closer to 0 representing regions of greater motion(perfusion) and 1 representing regions with no motion.

In certain aspects, this invention uses laser speckle imaging to providea real-time non-invasive means to inform the surgeons whether or not aparathyroid gland is still being perfused and is therefore viable.During a thyroid or parathyroid surgery, the invented apparatus ordevice acquires and processes images of the parathyroid gland. Thedevice comprises a 785 nm wavelength laser and a near-infrared camerawith a zoom lens, positioned above the surgical filed via an articulatedarm. The laser light is diffused onto the tissue surface and images areacquired by the camera. Images are acquired using a program developed oncommercially available software, and processed to produce specklecontrast image through the lab-developed dynamic link library filewritten in C++. This allows the speckle contrast images to be displayedto the surgeon in real-time (as they are acquired). In these specklecontrast images, perfused (and therefore viable) parathyroid glandsgenerally have low speckle contrast, while devascularized parathyroidglands have high speckle contrast.

The device and processing software have been proven feasible in a groupof patients. Speckle contrast images of vascularized parathyroid glandsand devascularized parathyroid glands are acquired duringparathyroidectomy, where darker regions represent areas of greater bloodflow and lighter regions represent areas of reduced blood flow. Thespeckle contrast images of parathyroid glands are compared against thesurgeon's assessment of whether or not the gland was devascularized,where the confidence level of the surgeon were also recorded. For largerparathyroids the images agree 100% with the surgeon's assessment,however the device did not function as well for smaller (normal) glands.In certain embodiments, some modifications to the device is made toincorporated a zoom lens, which is now getting better agreement forsmaller parathyroid glands.

Conventional laser speckle contrast imager appears less ergonomicallysuitable (more bulky) for use in the OR in the assessment of parathyroidglands than the invented LSCI device. According to the invention, theLSCI device can be combined with another lab-built device for detectingparathyroid gland using fluorescence, and marketed to endocrinesurgeons. In addition, the invention allows for a more compact finalproduct capable of assisting surgeons in first identifying parathyroidglands, and then assessing their viability.

These and other aspects of the present invention are further describedin the following section. Without intending to limit the scope of theinvention, further exemplary implementations of the present inventionaccording to the embodiments of the present invention are given below.Note that titles or subtitles may be used in the examples for theconvenience of a reader, which in no way should limit the scope of theinvention. Moreover, certain theories are proposed and disclosed herein;however, in no way should they, whether they are right or wrong, limitthe scope of the invention so long as the invention is practicedaccording to the invention without regard for any particular theory orscheme of action.

Example Intraoperative Assessment of Parathyroid Viability Using LaserSpeckle Contrast Imaging

This exemplary example was performed in patients undergoingthyroidectomies and parathyroidectomies by measuring the specklecontrast of parathyroid glands in vivo. Performance of LSCI wasevaluated in thyroidectomies, by grouping speckle contrast from normalfunctioning and compromised parathyroid glands according to thesurgeon's classification. Validation was performed inparathyroidectomies, where the state of vascularity of the parathyroidgland was controlled in glands planned for excision. Results demonstratethe effectiveness of LSCI for parathyroid gland assessment.

Materials and Methods:

LSCI System Design:

An LSCI system, as shown in FIG. 2, which is operably the operating room(OR), was developed according to one embodiment of the invention. In theexemplary embodiment, the LSCI system is mounted on an articulated armattached to a mobile cart. A 785 nm diode laser (Innovative PhotonicsSolutions, Monmouth Junction, N.J.) is coupled through a 400 μm fiberoptic patch cord (Thorlabs, Newton, N.J.) to a lens tube containing a 75mm focal length biconvex lens (Thorlabs, Newton, N.J.). This lensdiverges (diffuses) the laser light to a spot of about 8 cm diameter ata distance of about 45 cm from the edge of the lens. The irradiance atthe surface was measured to be about 0.6 mW/cm². A near-infraredoptimized camera (acA1300-60gmNIR, Basler AG, Ahrensburg, Germany)captures the images, which are focused onto the camera sensor by animaging lens system (Navitar 50 mm F/2.8, Navitar, Woburn, Mass.).Attached to the front end of the imaging lens system is a focus tunablelens (EL-16-40-TC-VIS-5D-M27, Optotune, Dietikon, Switzerland). Thisallows the images to be focused during each procedure from outside thesterile field as the height of the operating table may be slightlyadjusted during surgery. The field of view of the camera was measured tobe about 5 cm×6 cm. A 5 mW 660 nm laser pointer (DigiKey, Thief RiverFalls, Minn.) is attached such that its beam is co-localized with thecenter of the camera's field of view at a distance of 45 cm. The purposeof this laser pointer is to guide the surgeon in positioning the systemabove a parathyroid gland so that it is approximately in the center ofthe field of view. Images recorded by the camera are sent to a laptopcomputer for processing and display.

Ensuring Adequate Sampling of Speckle Pattern:

An important consideration when performing LSCI is that the specklepattern must be adequately sampled. The smallest speckle should be atleast twice the size of the sensor pixel in order to meet the Nyquistsampling criterion and avoid underestimating speckle contrast [25]. Totest whether the invented LSCI system met this criterion, an opticaltissue phantom made of polydimethylsiloxane (PDMS) with titanium dioxideto simulate tissue scattering (reduced scattering coefficient of 8 cm⁻¹)was illuminated and imaged with the LSCI device using different aperturesizes. The power spectrum was analyzed to ensure there was no aliasing.The iris size was set close to f/16 and locked in this position for theentire study. A well-defined energy band centered at the origin of thepower spectrum confirmed no aliasing. Although larger apertures also hadno aliasing, this aperture size was chosen because it also resulted invery little background from ambient lighting.

Patient Recruitment and Imaging Protocol:

This study was conducted in accordance with the Declaration of Helsinkiand its amendments. The study was approved by the Vanderbilt UniversityMedical Center (VUMC) Institutional Review Board (IRB). Patientsundergoing partial or total thyroidectomy at the Vanderbilt UniversityMedical Center were recruited and written informed consent was obtainedfrom each patient (n=20) prior to participation.

Images of parathyroid glands were recorded during the course of surgeryat the discretion of the surgeon. The surgeon first determined the stateof vascularity of the gland based on visual inspection, and thenpositioned the LSCI device above the surgical field so that the laserpointer beam was on the parathyroid gland. With the camera integrationtime set to about 50 ms to allow imaging with the room lights on, whitelight images were initially acquired to identify the location of theparathyroid gland. The laser pointer was turned off and the integrationtime was then set to 5 ms for the rest of the image acquisitions. Thisintegration time is within the range typically used for LSCI [17], andresults in the room lights contributing very little signal to the imagewhile effectively detecting the 785 nm speckle pattern. Next, the 785 nmlaser was turned on and images were acquired and sent to the computerfor real-time processing of speckle contrast images. Roughly fifteenseconds of acquisition were allowed for each gland to ensure that asufficient number of images was obtained. The surgeon was blinded to allimages during the surgery.

Validation of Technique:

Given that there is no gold standard for assessing parathyroid glandviability, validation of this technique was performed as follows.Patients undergoing parathyroidectomy at the VUMC were recruited andwritten informed consent obtained prior to participation following IRBapproval. In parathyroidectomies, a diseased parathyroid gland isplanned for removal. As part of standard procedure, the surgeon ligatedblood supply to the diseased parathyroid gland prior to excision. Thisprovides a controllable scenario for evaluating the capability of thedevice to detect parathyroid gland vascular compromise.

Speckle contrast images were acquired before and less than one minuteafter the surgeon ligated the blood supply to the gland, in preparationfor removal. To confirm removal of the hyperactive parathyroid gland,intraoperative measurement of PTH was performed before and 10 minutesafter excision of the gland. Changes in speckle contrast between thevascularized and ligated state were assessed.

Speckle Contrast Calculation:

The number of pixels over which spatial speckle contrast is calculatedis important, with too few pixels resulting in inaccuracy in contrastestimation while too many pixels sacrificing spatial resolution.Calculating speckle contrast over a 5×5 or 7×7 pixel region is generallyconsidered a good compromise [26]. In this exemplary embodiment, a 5×5pixel window was used in calculating speckle contrast. The window ismoved across the image of the acquired speckle pattern and at eachlocation, the speckle contrast is calculated as the standard deviationof pixel intensity values within the window divided by the mean(Equation 1). The resultant speckle contrast image has values that rangefrom 0 to 1, with values closer to 0 representing regions of greatermotion (perfusion) and 1 representing regions with no motion. Imageacquisition and display is performed through a custom LabVIEW program,while a custom dynamic link library file enables processing and displayat about 10 frames per second.

$\begin{matrix}{K_{s} = \frac{\sigma_{s}}{\langle I\rangle}} & (1)\end{matrix}$

Data Analysis:

Data was analyzed using MATLAB R2015a (The MathWorks Inc., Natick,Mass.). For each set of recordings on a single parathyroid gland, 20speckle contrast images were averaged after acquisition to improve thespatial resolution of the final image. To correct for slight movement ofthe surgical field during recordings, an image registration algorithmwas employed before averaging. Any image with sudden jerky motion(visually identified as a global sharp decrease in speckle contrast) wasexcluded from the averaging. The parathyroid gland was then demarcatedusing the “roipoly” function, avoiding bright spots caused by specularreflection, and the average speckle contrast within this region wascalculated. In certain embodiments of the device, polarizers are used toreduce specular reflection. The data was then grouped into vascularizedand compromised according to the surgeon's assessment of the gland.Compromised parathyroid glands were also further grouped into those thatthe surgeon decided to transplant and those that were left in place.Tests for statistical significance were performed using a two-sided twosample Student's t-test and p-values less than 0.01 were consideredstatistically significant.

Effect of Ambient Lighting on Speckle Contrast Images:

Performing measurements without the need to turn off the OR lights wouldminimize disruption to the surgical workflow. A microfluidic flowphantom made of PDMS and titanium dioxide to achieve a reducedscattering coefficient of 8 cm⁻¹ was used to evaluate the effect ofambient lighting on speckle contrast images in the laboratory. Thedevice had a 400 μm channel through which a 1% Intralipid(Sigma-Aldrich, St. Louis, Mo.) solution was flowed. Images wereacquired with the room lights on and then off, and 20 speckle contrastimages were averaged for each condition.

For one patient undergoing parathyroidectomy, two sets of measurementson one parathyroid gland were obtained to determine the effect of the ORlights on speckle contrast images. The surgeon first positioned thedevice so the parathyroid gland was in the field of view. Images wererecorded with the operating room lights on, but with the surgical lightsabove the operating table pointing away from the surgical field. Then,without moving the device, all operating room lights were turned off andanother set of images were obtained. For each condition, 20 specklecontrast images were averaged and the same region of interest was usedto calculate average parathyroid gland speckle contrast.

Results:

Device Design:

A portable, clinical LSCI device/system was developed and is shown inFIG. 2. In essence, the device includes a 785 nm coherent light sourceto diffuse light onto the surgical field, a near-infrared optimizedcamera to record the speckle pattern produced, and a computer to processand display images at 10 frames per second. The field of view wasmeasured to be about 5 cm×6 cm at a distance of 45 cm above theoperating table and the laser intensity at this distance was 0.6 mW/cm².

Effect of Ambient Lighting on Speckle Contrast Images:

Performing measurements without the need to turn off the operating room(OR) lights is essential so that any disruption to the surgical workflowis minimized. The effect of ambient lights on speckle contrast wasevaluated in the laboratory on a microfluidic flow phantom with a 1%Intralipid solution flowing through its 400 μm channel (FIGS. 3a and 3b). A rectangular region of interest crossing the channel was selectedand line profiles perpendicular to the channel within this region wereaveraged for both conditions, lights on and lights off. There was nosignificant difference in the decrease in speckle contrast when crossingthe channel, using a two-sample Student's t-test (p=0.19).

To determine how room lights would affect LSCI data acquired in theoperating room, the system was tested in vivo on a patient undergoingparathyroidectomy. One set of images was acquired with the room lightson and the surgical lights above the operating table pointed away fromthe surgical field, and another set with all lights off. For eachcondition, 20 speckle contrast images were averaged after acquisitionand the same region of interest was used to calculate averageparathyroid gland speckle contrast. There was a 1.7% decrease in theaverage speckle contrast value of the parathyroid gland when the ORlights were left on, compared to when they were off (FIGS. 3c-3f ). Thisis to be expected since OR lights have a broad frequency spectrum [24]and therefore do not produce a speckle pattern. The uniform lightingfills in dark spots in the speckle pattern generated by the laser,thereby reducing the contrast. However, the magnitude of this decrease(about 0.002) was miniscule compared to the possible range of specklecontrast values (0 to 1). Additionally, this value is less than 2% ofthe range of average parathyroid gland speckle contrast obtained in thisstudy. These results indicated that the performance of the LSCI systemis not affected by ambient light and validates its application in theoperating room with the OR lights on but pointed away from the patientduring image acquisition.

Vascularized vs. Compromised Parathyroid Glands:

The LSCI system was tested in twenty patients undergoing thyroidectomyat Vanderbilt University Medical Center. Speckle contrast images ofparathyroid glands were acquired during the course of surgery and at thediscretion of the participating surgeon. The surgeon's visual assessmentof the gland's viability (without input from speckle contrast images)was recorded at the time of image acquisition for each gland. FIG. 4shows examples of parathyroid glands considered vascularized andcompromised. The left column shows white light images of the surgicalfield, and the right column shows the corresponding speckle contrastimage (average of 20 images). Parathyroid glands are indicated with awhite ellipse. As these images show, parathyroid glands consideredvascularized by the surgeon have lower speckle contrast than thoseconsidered to be compromised.

The average speckle contrast within each parathyroid gland wascalculated, avoiding bright spots of specular reflection. This data wasthen grouped according to the surgeon's visual assessment ofvascularity, which served as the gold standard. Using a two-sampletwo-sided Student's t-test, a statistically significant difference(p<0.0001) was observed in the speckle contrast between glandsconsidered vascularized versus compromised as determined by the surgeon(FIG. 5a ). Within the compromised group, there were 5 glands that weretransplanted, and 22 others that the surgeon decided could be left inplace without significant adverse effects to the patient. While the meanspeckle contrast was higher in the transplanted group, this differencewas not found to be significant using a two-sample t-test. These resultsare shown in FIG. 5 b.

Using speckle contrast as a classifier to distinguish between thevascularized and compromised parathyroid glands, a receiver operatingcharacteristic (ROC) curve was generated with an area under the curve of0.935 (FIG. 5c ). The optimum threshold for distinguishing between thetwo groups was found to be 0.09, which resulted in a sensitivity of92.6% ( 25/27 compromised glands correctly identified) and a specificityof 90.6% ( 29/32 vascularized glands correctly identified). From this,the overall accuracy was calculated to be 91.5%.

Validation of Technique:

Given that there is no gold standard for assessing parathyroid glandviability and these normal functioning glands cannot be excised forhistological validation without compromising patient care, validation ofthe LSCI system for this application was performed on eight patientsundergoing parathyroidectomy, where a diseased parathyroid gland isplanned for removal. As part of standard procedure, the surgeon ties offall blood supply to the gland prior to excision. This provides acontrollable scenario for evaluating the capability of the device todetect when a parathyroid gland is compromised as well as to determinethe detection limit (or time) of the system. To confirm removal of thehyperactive parathyroid gland, intraoperative measurement of PTH isroutinely performed before and 10 minutes after excision of the gland.

An example of a hypercellular diseased parathyroid gland marked forremoval is shown in FIG. 6. Again, the left column shows white lightimages while the corresponding speckle contrast images are in the rightcolumn. Images on the top row are of the gland before the surgeon tiedoff the blood supply. Images on the bottom row were taken on average 30seconds after the surgeon tied off the blood supply to the gland.According to the surgeon and as seen in the white light image, thisgland did not appear visually different from its initial state. However,there is a clear change in the speckle contrast images. In all cases,speckle contrast increased by a minimum of 18% after the surgeon tiedoff the blood supply (data shown in Table I; mean increase of 0.043).Further, post-excision intraoperative PTH was also lower thanpre-excision PTH, confirming removal of the diseased gland. PTH data wasnot acquired for two glands of patient 5 because removal of the firstdiseased gland resulted in PTH falling within the acceptable range(10-70 pg/mL) and all glands were diseased (Roche Elecsys 2010).

TABLE I Summary of data from excised diseased parathyroid glands. In allcases there was a large increase in speckle contrast seconds afterligation of the blood supply to the gland. There was also a decrease inPTH related to the number of diseased glands removed. In patient 5, LSCIdata was obtained from 3 glands that were excised, however PTHmeasurement was not performed after removal of glands 2 and 3.Post-ligation Pre-excision Post-excision Patient Pre-ligation speckle[PTH] [PTH] No. speckle contrast contrast (pg/mL) (pg/mL) 1 0.076 0.12686 26 2 0.057 0.094 142 34 3 0.062 0.131 172 32 4 0.074 0.130 119 115  40.069 0.119 115 45 5 0.064 0.093 151 53 5 0.048 0.085 53 N/A 5 0.0840.113 N/A N/A 6 0.063 0.092 130 31 7 0.067 0.115 76 26

Discussions:

This exemplary embodiment of the invention demonstrates the capabilityof LSCI to intraoperatively distinguish between vascularized andcompromised parathyroid glands. These measurements can be performed inreal-time and with the operating room lights on, minimizing disruptionto the surgical workflow. The average speckle contrast value ofvascularized parathyroid glands was significantly lower than that of thecompromised parathyroid glands, consistent with the understanding thatreduced blood flow causes less blurring of the speckle pattern andtherefore a higher speckle contrast [17]. Using the ROC curve in FIG. 5c, a speckle contrast value of about 0.09 was found to be optimal indistinguishing between the two groups with 91.5% accuracy. The abilityof LSCI to accurately detect compromised vascularity in the parathyroidgland was validated in the parathyroidectomy cases. These images furthershow that this device is able to detect changes in speckle contrastwithin seconds of devascularization. This is much earlier than a surgeonwould be able to identify based on visual inspection alone which relieson the gland turning dark with deoxygenated blood and losing turgor, aprocess which can take several minutes and is often missed. Unlike othertechniques that have been used to assess parathyroid gland viability,LSCI can be performed non-invasively, with no risk of damage to theparathyroid gland by physical trauma, nor damage to any nearby tissues.It does not require administration of an exogenous contrast agent, whichcan take 1-2 minutes to achieve optimum circulation [16]. Additionally,multiple measurements can be made on the same gland without risk oftoxicity. The device enables real-time assessment by processing anddisplaying speckle contrast images at 10 frames per second. The imagesshown in the disclosure were created after acquisition by averagingindividual frames in order to improve spatial resolution. However,quantitative information on a region of interest can also be displayedin real-time if desired as this information is generated concurrentlywith imaging. This technique can be performed with the room lights on,only requiring that the lights above the operating table be pointed awayfrom the surgical field.

The biggest challenge facing this study is the fact that the currentgold standard for assessing parathyroid gland viability intraoperativelyrelies on the surgeon's experience which is highly subjective. Theparticipated surgeon has multiple years of experience in this field andis therefore more likely than not to provide accurate assessments.However, thyroidectomies are routinely performed by general surgeons andresidents, and a higher error rate is likely, indicating the need forobjective assessment of parathyroid viability. These results demonstratethat LSCI has the potential to become the gold standard in this field.

In the absence of an objective gold standard to validate the performanceof this device, paired measurements were made in parathyroidectomy caseswhere the state of vascularity was controlled. It should be noted thatthe PTH measurements made after excision of the glands are not meant todirectly correlate with speckle contrast values but are simply toconfirm that the excised tissues are diseased parathyroid glands. A morerobust validation method would be to measure PTH after tying off thegland but before excision. However, this was not feasible as it takesabout 5-10 minutes for PTH levels to stabilize to a new value and such aprocedure would extend OR time and lead to added risk for the patient.

While this device performed with high accuracy in distinguishing betweenvascularized and compromised parathyroid glands in thyroidectomies,there were 5 instances of disagreement with the surgeon. One case shedlight on a possible reason for this disagreement. This particularparathyroid gland was evaluated by the surgeon to be initially wellvascularized, however its high speckle contrast value suggestedotherwise as observed in FIG. 7b . After 15 minutes, the surgeonre-evaluated this gland as devascularized and transplanted it, withspeckle contrast images agreeing with this assessment (FIG. 7d ). Thiscase further demonstrates the ability of LSCI to detect vascularcompromise before it is visually apparent to the surgeon.

An interesting observation was that of the 27 glands the surgeonconsidered to have suffered vascular compromise, only 5 wereautotransplanted. The rest were considered capable of recovery. However,no significant differences in speckle contrast were observed betweenthese two groups (though the small sample size for the transplantedgroup will make any differences difficult to identify). This warrantsfurther investigation with a larger study to identify what is trulyviable. Future studies will additionally acquire pre- and post-surgeryPTH measurements in patients with autotransplanted and intactparathyroid glands so that patient outcome may be correlated withspeckle contrast images. This will enable answering questions such as:“Should all glands with speckle contrast above a given threshold beautotransplanted in order to avoid hypoparathyroidism?”, and/or, “Is itsafe to leave suspicious-looking glands in place if at least oneparathyroid has speckle contrast below this threshold?”

It should be noted that LSCI senses motion, therefore these measurementsare highly susceptible to random movement of the surgical field causedby the patient's breathing and movement of the hands holding retractorsto expose the surgical field. Image registration was used to alignimages prior to averaging, however this does not avoid the artificialdecrease in speckle contrast introduced to a single frame by suchmotion. For reference, the average speckle contrast of an excisedparathyroid gland placed on a stable surface in the same operating roomwas measured to be 0.2, whereas the highest value obtained in vivo wasabout 0.13. In spite of this unavoidable source of error, very distinctdifferences in speckle contrast were obtained as demonstrated by theparathyroidectomy data (Table I). To improve the accuracy of the finalimage, any image with jerky motion (visually identified as a globalsharp decrease in speckle contrast) was excluded from the averaging.This was done manually due to the rarity of the event. In the future,should it be required, an algorithm could be employed to automate thisprocess and reject speckle contrast images with values a specifiedpercentage below the mean. Regardless of these limitations, this studyclearly shows the applicability of LSCI as a real-time, contrast-freeand objective guidance tool for assessing parathyroid gland viabilityintraoperatively. It will be of particular benefit to less experiencedsurgeons and residents, and could reduce hospitalization and long-termmedication costs associated with post-surgical hypoparathyroidism. Thisdevice could also have applicability for other clinical procedures wherethere is the need to non-invasively investigate the presence of tissueperfusion.

In sum, the invention presents LSCI as a potential real-time,non-invasive, contrast-free and objective tool for guiding surgeonsduring thyroid surgeries to assess the viability of parathyroid glands.The device according to embodiments of the invention can provide thisinformation to surgeons with minimal disruption to the surgicalworkflow, and can detect vascular compromise in its early stages beforeit becomes evident to the surgeon's eye. This tool can thereforesignificantly minimize post-surgical hypoparathyroidism and itsconsequent morbidities and costs.

The foregoing description of the exemplary embodiments of the presentinvention has been presented only for the purposes of illustration anddescription and is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many modifications andvariations are possible in light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toactivate others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the foregoing description and the exemplary embodiments describedtherein.

LISTING OF REFERENCES

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What is claimed is:
 1. A method for intraoperative assessment ofparathyroid gland viability in a surgery, comprising: diffusing a beamof light onto a tissue surface of a parathyroid gland of a patient toilluminate the tissue surface; acquiring images of the illuminatedtissue surface, wherein each of the acquired images comprises a specklepattern; and processing the acquired images to obtain speckle contrastimages for the intraoperative assessment of parathyroid gland viability.2. The method of claim 1, wherein the beam of light is emitted from alight source.
 3. The method of claim 2, wherein the light sourcecomprises an infrared laser.
 4. The method of claim 1, wherein saidacquiring the images of the illuminated tissue surface is performed witha detector.
 5. The method of claim 4, wherein the detector comprises acamera.
 6. The method of claim 5, wherein the camera comprises aninfrared camera or a near-infrared camera.
 7. The method of claim 5,wherein the detector further comprises a focus tunable lens attached tothe front end of the camera.
 8. The method of claim 1, wherein in thespeckle contrast images, a perfused parathyroid gland has low specklecontrast, and a devascularized parathyroid gland has high specklecontrast.
 9. The method of claim 1, wherein said processing the acquiredimages comprises calculating a plurality of speckle contrasts from theacquired images of the parathyroid gland.
 10. The method of claim 9,wherein said calculating plurality of speckle contrasts comprises:defining a window with a number of pixels over which a speckle contrastis to be calculated; moving the window across the acquired image of thespeckle pattern; and at each location, calculating the speckle contrastas a standard deviation of pixel intensity values σ_(s) within thewindow divided by a mean intensity value

I

as follows: $K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$ wherein theresultant speckle contrast image has values that range from 0 to 1, withvalues closer to 0 representing regions of greater motion (perfusion)and 1 representing regions with no motion.
 11. The method of claim 1,further comprising: displaying the speckle contrast images of theparathyroid gland in real-time.
 12. An apparatus for intraoperativeassessment of parathyroid gland viability in a surgery, comprising: alight source for emitting a beam of light; a diffuser coupled to thelight source for diffusing the beam of light onto a tissue surface of aparathyroid gland of a patient to illuminate the tissue surface; adetector for acquiring images of the illuminated tissue surface, whereineach of the acquired images comprises a speckle pattern; and acontroller arranged to operate the detector to acquire the images of theilluminated tissue surface, receive the acquired images from thedetector, and process the acquired images to obtain speckle contrastimages for the intraoperative assessment of parathyroid gland viability.13. The apparatus of claim 12, wherein the light source comprises aninfrared laser.
 14. The apparatus of claim 12, wherein the diffusercomprises a biconvex lens.
 15. The apparatus of claim 12, wherein thedetector comprises a camera.
 16. The apparatus of claim 15, wherein thecamera comprises an infrared camera or a near-infrared camera.
 17. Theapparatus of claim 15, wherein the detector further comprises a focustunable lens attached to the front end of the camera.
 18. The apparatusof claim 12, further comprising a laser pointer arranged in relation tothe detector such that its beam is co-localized with a center of thefield of view of the detector at a distance.
 19. The apparatus of claim12, wherein in the speckle contrast images, a perfused parathyroid glandhas low speckle contrast, and a devascularized parathyroid gland hashigh speckle contrast.
 20. The apparatus of claim 12, wherein saidprocessing the acquired images of the parathyroid gland by thecontroller is performed with calculating a plurality of specklecontrasts from the acquired images of the parathyroid gland.
 21. Theapparatus of claim 20, wherein said calculating a plurality of specklecontrasts from the acquired images of the parathyroid gland is performedwith: defining a window with a number of pixels over which a specklecontrast is to be calculated; moving the window across the acquiredimage of the speckle pattern; and at each location, calculating thespeckle contrast as a standard deviation of pixel intensity values σ_(s)within the window divided by a mean intensity value

I

as follows: $K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$ wherein theresultant speckle contrast image has v lues that range from 0 to 1, withvalues closer to 0 representing regions of greater motion (perfusion)and 1 representing regions with no motion.
 22. The apparatus of claim 1,further comprising a display for displaying the speckle contrast imagesof the parathyroid gland in real-time.
 23. A method for intraoperativedetection of parathyroid gland viability in a surgery, comprising:obtaining speckle contrast images of a parathyroid gland of a patent;and displaying the speckle contrast images of the parathyroid gland inreal-time.
 24. The method of claim 23, wherein said obtaining thespeckle contrast images of the parathyroid gland of the patentcomprises: diffusing a beam of light onto a tissue surface of aparathyroid gland of a patient to illuminate the tissue surface;acquiring images of the illuminated tissue surface, wherein each of theacquired images comprises a speckle pattern; and processing the acquiredimages to obtain speckle contrast images.
 25. The method of claim 24,wherein in the speckle contrast images, a perfused parathyroid gland haslow speckle contrast, and a devascularized parathyroid gland has highspeckle contrast.
 26. The method of claim 24, wherein said processingthe acquired images comprises calculating a plurality of specklecontrasts from the acquired images of the parathyroid gland.
 27. Themethod of claim 26, wherein said calculating plurality of specklecontrasts comprises: defining a window with a number of pixels overwhich a speckle contrast is to be calculated; moving the window acrossthe acquired image of the speckle pattern; and at each location,calculating the speckle contrast as a standard deviation of pixelintensity values σ_(s) within the window divided by a mean intensityvalue

I

as follows: $K_{s} = \frac{\sigma_{s}}{\langle I\rangle}$ wherein theresultant speckle contrast image has values that range from 0 to 1, withvalues closer to 0 representing regions of greater motion (perfusion)and 1 representing regions with no motion.
 28. An apparatus forintraoperative detection of parathyroid gland viability in a surgery,comprising: means for obtaining speckle contrast images of a parathyroidgland of a patent; and displaying the speckle contrast images of theparathyroid gland in real-time.
 29. The apparatus of claim 28, whereinsaid means for obtaining the speckle contrast images comprises: a lightsource for emitting a beam of light that is diffused onto a tissuesurface of the parathyroid gland of the patient to illuminate the tissuesurface; a detector for acquiring images of the illuminated tissuesurface; and a controller arranged to operate the detector to acquirethe images of the illuminated tissue surface, receive the acquiredimages from the detector, and process the acquired images to obtain thespeckle contrast images.
 30. The apparatus of claim 29, wherein thelight source comprises an infrared laser.
 31. The apparatus of claim 29,wherein the beam of light is diffused onto the tissue surface of theparathyroid gland by a diffuser including a biconvex lens.
 32. Theapparatus of claim 29, wherein the detector comprises a camera.
 33. Theapparatus of claim 32, wherein the camera comprises an infrared cameraor a near-infrared camera.
 34. The apparatus of claim 32, wherein thedetector further comprises a focus tunable lens attached to the frontend of the camera.
 35. The apparatus of claim 29, wherein in the specklecontrast images, perfused parathyroid gland has low speckle contrast,and a devascularized parathyroid gland has high speckle contrast.